It is a problem in the field of fluid and solid mineral extraction to efficiently extract subsurface components in subsurface deposits, reservoirs, or fields. For example, the oil industry typically produces only about one-third of the original oil in place (“OOIP”) from a field before it is considered “depleted.” The termination of recovery operations from depletion is really driven by declining oil recovery until an economic limit is approached and the recovery operation is terminated or mothballed. Thus, the majority of oil remains un-recovered though discovered, identified and with direct physical access by existing wells. World oil demand is expected to jump an estimated 50% by 2025, according to the U.S. Department of Energy, and it is most unlikely that current production and extraction technology will be able to supply this increased demand of the world's growing requirements and economies.
Many extraction technologies have been employed to improve the recovery from known and developed fields as they near their economic production limit. For example, the improved oil recovery (“IOR”) processes involve two general technology pathways: solvent or immiscible fluid displacement methods. Solvent based methods involve the injection of hydrocarbon gases, carbon dioxide, or other substances that rely on the injected fluid becoming miscible and dissolving into the liquid hydrocarbon. This technological pathway is expensive due to the costs of producing, processing, transporting, compressing, injecting, and recycling of valuable substances to recover additional hydrocarbons.
Immiscible displacement technologies, such as water flooding, use water directly as a displacement fluid. To release incremental oil from a reservoir, externally derived substances, such as chemicals, surfactants, polymers, and alkaline materials (among others) are often added to change the fluid and rock petrophysical properties during a water flood. These chemicals change the flow properties and may improve the microscopic displacement by increasing the water wettability at the pore level. At the pore scale, rock-fluid interactions and solid-liquid surface effects become a significant factor in water wettability modifications. Increasing the water wettability of a substrate will release additional oil from pore surfaces that can be recovered by the general water flood process.
Surfactants have been used to improve displacement-based technologies by altering the flow and properties at the solid-liquid interface. The surfactant penetrates the pore scale internal structure to reduce the amount of oil trapped by capillarity, other surface-liquid forces and liquid-liquid forces. The interfacial tension between the water and oil phases is reduced, thus increasing the water wettability of the substrate. The incremental displaced oil is then captured by the general water flood process and transported for recovery. The reduction of interfacial tension increases the water saturation as smaller pore spaces undergo water imbibition that enhances the direct expulsion of oil from a pore space. This results in pore and capillary scale mobilization and displacement of the oil phase and improves oil displacement efficiency. Various other benefits may occur depending on the chemical interaction of the surfactant and the hydrocarbon phase. These include modification of the multi-phase flow mobility by increasing rock-water wettability and changes in the relative permeability relationship. One limitation is the significant cost of surfactants in relation to the benefits gained. Technical limitations of this approach include surfactant adsorption on the rock/solid interface and the effect of calcium/magnesium (e.g., hard water) interactions in the subsurface. This latter effect can simply be described by the reduction of surfactant effectiveness in the presence of hard water.
Polymers have been used to improve the displacement process by modifying the two-phase mobility of the injected fluid, such as water, thus increasing its fluid viscosity to achieve a more uniform displacement front and improved volumetric/macroscopic fluid sweep efficiency. Polymers generally do not result in a change in the rock wettability or change the residual non-wetting phase saturation relative to the permeability endpoint. As with other chemical additive methods, the cost of the polymers is a significant disadvantage. The polymers must be precisely mixed to generate the desired effect in the subsurface. Additional limitations exist from adsorption of the polymer by the substrate and ineffectiveness in reducing oil saturation.
Alkaline substances entrained in the injected fluid have also been used to improve oil recovery. Alkaline flooding or high pH methods typically use hydroxide anions (OH−) or weakly dissociating acids to reduce the concentration of hydrogen ions (H+) from the solution. The introduction of a high pH solution into a reservoir results in a disassociation of a hydroxyl-containing species that preferentially bind hydrogen ions and the creation of a surfactant as a reaction occurs between the oil and the alkaline fluid. An increase in water wettability of the porous media directly displaces hydrocarbons from the porous media. Alkaline flooding uses chemicals like sodium hydroxide, sodium orthosilicate and sodium carbonate to generate solutions having a sufficiently high pH. A typical alkaline flood design may use concentrations of up to 5% and a slug size of 0.2 pore volumes to achieve a beneficial effect. The quantity of chemicals needed for this application is significant and the costs of implementation reflect this requirement. Technical limitations of this approach (beyond the logistics of substantial chemical handling) include consumption of the alkaline materials by the geologic media, requiring additional chemicals to maintain the expected benefit.
Other chemical methods include petroleum sulfonates that are produced by combining crude oil or intermediate molecular weight hydrocarbons with SO3 gas to yield a highly acidic solution that in turn produces anionic surfactants. These anionic surfactants are dissolved in an aqueous solution, thus producing a cation and a monomer, which forms a micelle. When the micellar solution contacts the oleic phase, the surfactant accumulates in the pore, lowering the interfacial tension between the oil and water phases. This results in an increase in the water wettability and the displacement of oil from the pore. As with other techniques, a limitation of this approach is the significant cost of producing and transporting the sulfonates in relation to the benefits gained. One of the technical limitations is the stability of the micelle during flood displacement.
Low salinity flooding has been used to improve oil recovery by diluting the connate brine (existing in-situ brine within the strata) with lower salinity water. The lowering of salinity increases the pH and increases water wettability and the subsequent displacement of hydrocarbons from the porous media. This process has been noted to act similar to an alkaline flood by increasing the water wettability of the rock-liquid interface. The reduction of salinity can be accomplished by dilution or more commonly by the use of reverse osmosis (RO) processes. This approach is both capital intensive and has a significant operational cost burden for the duration of the operation. Technical limiting factors are the large capacity of the RO systems required and the limitation of the dilution effect within the formation.
While the above examples are related to oil recovery, other fluid and solid mineral resource recoveries are faced with similar issues. Mineral recovery efficiency is hampered by both technical and economic hurdles. This has impeded the overall development of the resource endowment and improvements in extraction efficiency.
Current state-of-the-art processes rely on the introduction of externally derived materials (e.g., chemicals) to alter the bonding state of the solid-liquid interface of solid mineral and other components in the subsurface to release/recover the components of interest. These applications have increased recovery efficiencies, but are approaching both technical and economic limits. The introduction of external materials added for extraction may have unwanted (physical, geochemical, petrophysical or other) side effects that limit extraction efficiency and/or create environmental damage. This invention will reduce capital and operating costs while improving the recovery of subsurface components.